Apply type optimizations across local function calls#2100
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jhogberg merged 8 commits intoJan 24, 2019
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A switch is equivalent to a series of '=:=', so we have to subtract each value individually from the type. Subtracting a join risks removing too much type information, and managed to narrow "number" into "float" in the attached test case.
If the match instruction was already marked as a skip, we'd ruin its argument list.
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9daffa0 revealed some funny side-effects from propagating the 'none' type across functions. I'm working on fixing them but it might take some time. |
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This serves as a base for the upcoming module-level type optimization, but may come in handy for other passes like beam_ssa_funs and beam_ssa_bsm that have their own ad-hoc implementations.
This commit lets the type optimization pass work across functions, tracking return and argument types to eliminate redundant tests.
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The `error_handler` module in the Kernel application has a call to the
`int` module in the Debugger application. That call is only there to
make the Debugger work. To avoid that Xref sees Debugger as a
dependency for Kernel, the call to the `int` module is obfuscated in
the following way:
breakpoint(Module, Func, Args) ->
(int()):eval(Module, Func, Args).
int() -> int.
That is, the call will show up as a call to an unknown module in
Xref.
With the improved whole-module type analysis introduced in
294d66a (erlang#2100), the compiler sees through the obfuscation
and rewrites the code to:
breakpoint(Module, Func, Args) ->
int:eval(Module, Func, Args).
It would be fun to solve this issue by introducing further obfuscations,
but such tricks could stop working in the future when the compiler is
improved. Instead, turn off whole-module type analysis by compiling
the module with the `no_module_opt` option.
Resolves erlang#4546
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The current type pass works on a per-function level and assumes that every argument and return value could be anything, which means they have to be type-checked before they're used. This is a bit inefficient as most functions always return something of the same type, and their argument types seldom differ.
This PR makes the type pass track the return and argument types of local functions, letting us eliminate many redundant type checks.